Abstract Body: Introduction: Mitochondria are vital energy producers in the heart, thus requiring fine-tuned regulation. Mitochondrial proteins are regulated by post-translational modifications, such as phosphorylation, prompting our investigation of the mitochondrial phosphatase PPTC7 in cardiac homeostasis.
Goal: Hyperphosphorylation of mitochondrial proteins is linked to heart disease, yet how these modifications impact cardiac pathology remains unclear. By modulating mitochondrial phosphatase PPTC7, our goal is to determine how hyperphosphorylation of mitochondrial proteins may impact the development of cardiovascular disease.
Hypothesis: BNIP3 is a mitophagy receptor that is overexpressed and hyperphosphorylated in Pptc7 knockout (KO) murine hearts, which is shown in cell culture models to induce mitophagy. As the overexpression of BNIP3 in the heart is strongly linked to the development of dilated cardiomyopathy and phosphorylation of the BNIP3 is linked to its stability, we hypothesized that cardiac-specific Pptc7 KO mice would develop dilated cardiomyopathy due to excessive BNIP3-mediated mitophagy.
Methods: Using a cardiomyocyte-specific Pptc7 KO mouse model, we performed echocardiography, histology, transmission electron microscopy, and oxygen consumption assays to test how the loss of Pptc7 affects heart form and function, mitochondrial ultrastructure, and mitochondrial function.
Results: Cardiomyocyte-specific Pptc7 KO animals develop age-dependent dilated cardiomyopathy that progresses to fatal heart failure with reduced ejection fraction and cardiac cachexia at 10 months. On a histological level, Pptc7 KO animals exhibit disorganized cardiomyocytes and cardiac fibrosis, indicative of cardiac injury. Using electron microscopy to examine organellar ultrastructure, Pptc7 KO hearts revealed an increase in mitochondrial area. This abnormal morphology was consistent with intrinsic dysfunction, as isolated mitochondria from Pptc7 KO hearts show reduced oxygen consumption.
Conclusion: In the future, we will directly test the role of mitophagy and BNIP3 in these phenotypes using additional mouse models. Since BNIP3 levels are elevated in heart failure, this project will reveal the importance of limiting or reversing BNIP3-mediated mitophagy in human patients.